/**
*      author: Y_Yao
*      created: 2025-03-07 22:42:24
**/

#include<bits/stdc++.h>

#define int LL
using namespace std;
using LL = long long;
const LL LLINF = 1e18;
const int INF = 0x3f3f3f3f;
const int N = 2e5 + 7;
int a[N],sum[N];
int n,m;

void solve()
{
    cin >> n >> m;
    for(int i = 1;i <= n;i++)
    {
        cin >> a[i];
        sum[i] = sum[i-1] + a[i];
    }

    int ans = -LLINF;
    int prev = 0;
    for(int i = 1;i <= m;i++)
    {
        prev += a[i] * i;
    }
    ans = prev;
    for(int i = 2;i <= n - m + 1;i++)
    {
        int cur = prev;
        cur -= sum[i - 1 + m - 1] - sum[i - 2];
        cur += a[i + m - 1] * m;
        prev = cur;
        ans = max(cur,ans);
    }
    cout << ans << endl;
}

signed main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);

    int t = 1;
    //cin >> t;
    while(t--)
    {
        solve();
    }
    return 0;
}